It is already known that a deformation sensor may be used in a side part of a motor vehicle for sensing a side impact, to record plastic deformation of the outer skin on the side part. A deformation sensor element of the deformation sensor is attached to a bottom plate of the sensor, which is in turn mounted on a side part reinforcing element using riveted connections. In addition, an analyzer unit which is connected to the deformation sensor and a digital interface which transmits data to a control unit for restraint devices are also provided on the bottom plate of the sensor.
The device according to the present invention for sensing a side impact in a motor vehicle has the advantage over the related art that it is possible to check the riveted connections for integrity and solidity during the lifetime of the vehicle. To do so, a static output signal of the deformation sensor is used to advantage and is compared with a predetermined threshold value to ascertain whether the mechanical strength of the riveted connections is still within predetermined parameters. Mechanical strength of the riveted connections is an absolute necessity for correct functioning of the deformation sensor for sensing a side impact, so that according to the present invention, inadequate strength of the two riveted connections leads to a warning. Such a warning is then output over an airbag warning lamp, for example.
It is especially advantageous that the sensor bottom plate is made of a metal, preferably a steel, having a higher thermal expansion coefficient than the metal or steel of the side part reinforcing element. As in the known bimetal effect, this results in a temperature-dependent static bending of the bottom plate of the sensor with respect to the side part reinforcing element. This then yields a static signal of the deformation sensor. According to the present invention, this static signal is then compared with a predetermined threshold value, which leads to a warning if the static signal is below the threshold and if the temperature in the side parts is above room temperature.
In addition, it is advantageous that the deformation sensor element is designed as a strain gauge sensor. Most serious side impact situations in terms of injury are detectable after a period of only 3 to 5 ms by using a strain gauge sensor. The deployment threshold of an acceleration sensor which is provided on the B pillar of a motor vehicle, for example, may be lowered immediately with a signal generated by the strain gauge sensor, so that the side airbags for protecting the head and chest area of the vehicle passengers may be activated promptly. Strain gauge sensors may be riveted in an advantageous manner to the deformation body, the onset of whose elastic deformation is to be sensed, so that defective components can be simply replaced, but the part to be monitored, i.e., the side part of a vehicle, may remain in use. To this end, the strain gauge sensor may be easily riveted to a side part reinforcement, e.g., a reinforcing pipe, in the door cavity, thereby eliminating complicated direct welding or gluing onto the deformation part. It is advantageous here that the strain gauge or deformation sensor is usable for side impact sensing in combination with at least one acceleration sensor, so that the acceleration sensor here functions as a plausibility sensor. As explained above, this is able to make side impact sensing faster and more reliable. A shortened period of time until side impact sensing is also possible in combination with a pressure sensor.
In addition, it is advantageous that the deformation sensor is welded to the sensor bottom plate. This is a simple and reliable method of joining.
The temperature sensor together with the analyzer unit may be manufactured to advantage as a chip, so that no additional space on the sensor plate need be provided for the temperature sensor.
It is also advantageous that the sensor bottom plate is designed to be flexurally slack, so that the sensor bottom plate has only an insignificant influence on deformation of the side part reinforcing element. Therefore, this does not have any negative effect on the measurement by the deformation sensor.
Finally, it is also advantageous that a flexible circuit board is attached to the top side of the sensor bottom plate as a connection carrier for the deformation sensor, the analyzer unit and the temperature sensor.